Overview of the three major systems of the aSNOM. Mechanical setup: S: sample stage, C: AFM cantilever, M: mirror, PSD: position sensitive detector, : noncontact mode oscillation frequency of the cantilever, PM: periscope mirror, and AL: aspheric focusing lens. Optical setup: LS: laser source, BS: beam splitter, BP: beam preparation, M: mirror, NFO: near field optical interaction region, and D: detector. Electronic setup: : oscillation frequency of the AFM cantilever, : harmonic index, : AOM drive frequency, and SBF: sideband filter.
Upper half: Oblique incidence illumination of the tip apex with a focused laser beam. The cantilever body limits the incidence angle. Lower half: Cantilever tip profiles from three different suppliers.
Scheme of the interferometric optical detection. L: lens, BS: beam splitter, AOM: acousto-optic modulator, I: iris stop, M: mirror, PD: photodiode, VA: variable attenuator, P: polarizer, A: analyzer, and D: detector.
(a) Easy alignment of an AdvancedTEC tip with the optical focus. Accumulating scans at several values allows us to map the entire focal volume. (b) Focal spot scan of a area at the optimum position.
Amplitude and phase scattered by a Au coated Si tip while a thick Au film surface is approached from below. An optical near field contribution is detected at distances from the Au surface.
aSNOM scans of sample area at demodulation. The upper line is the set of images with normal tip apex centered illumination. The lower line is obtained under identical experimental conditions, except for the excitation beam being focused at the top of the tip shaft, not its apex.
(a)–(d) Optical amplitude images of a area of Ag colloids on a Si substrate acquired in high-speed overview tip-scanning mode. (a) , with the sample retracted, shows the field strength envelope in the optical focus. (b)–(d), with the sample in contact, show the , , and optical amplitudes recorded at demodulation frequencies of 1, 2, and . (e) and (f) optical amplitude images of a thick Au pattern on a thick oxide substrate on Si, obtained by scanning (e) the sample and (f) the tip.
A scan of nanosphere lithographically patterned Au on glass sample. On the left, optical amplitude, optical phase, and topography information are displayed for the horizontal line cut indicated on the right images.
Spatial resolution studies with aSNOM. (a) Topography (top) and (bottom) of a scan of nominally diam Ag colloids deposited on Si. Plots along the lines marked in the images are displayed on the right. (b) Optical (left) and topography (right) of a scan of overgrown Si substrate edge. Line plots given at the bottom of each image belong to the marked positions in the images.
A optical phase image of the same sample as in Fig. 9(a). On the right are the line scan data belonging to the marked positions on the image.
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